Generating and transmitting system



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. M. K. AKERS GENERATING AND TRANSMITTING SYSTEM Filed Dec. 31. 1919 sa o Z ago spa

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rates MILTGIT K. AKEBS, OF EAS'I ORANGE, IJEWJERSEY, ASSIGNOR- T VJESTERN ELECTRIC CDMEFAITY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

' ennnna'rine AND TRANSMITTING SYSTEM.

Application filed December 31, 1919. Serial No. 348,555.

This invention relates to signaling systems and more particularly to oscillators of the discharge type wherein an electron or other dischargedevice such as a vacuum tube having an anode, a cathode, and an impedancecontrolling element isprovidedfor use in such systems to generate oscilllations.

When certain circuit arrangements are connected to such discharge devices for the generation of oscillations parasitic oscillations tend to be set up owing to the internal capacity of the tubeor the leads thereto acting as a capacity in combination with one or more other elements 0t. thecircuit to pro- 7 duee a frequency determining oscillation circuit. At frequencies bearing a certain relation to the parasitic frequency, the power output at the desired frequency is very much reduced. in some instances the vacuum tube ceases to produce oscillations. of the desired frequency at certain adjustments owing to the absorption of energy by the parasitic oscillations. Thus with a certain transmitting apparatus while satisfactory transmission can be carried on at one wave length, upon changing to another wave length, the power output will tall to an insufiicient value or the apparatus will become inoperative, unless cumbersome and time consuming re-ad'just ments are made. One object ot' the invention is to provide means whereby when the wave length is changed, the power output may be maintained at a high value.

In one form'the invention includes a small variable condenser connected between the. grid and the anode otthe oscillating tube whereby the desired result is obtained. In another form a condenser is shunted across the output primary coil of the oscillator.

The inventionalso includes means for decreasing the power loss of an oscillator by improving the power factor of the plate current through the tube.

The invention also includes a novel form of variometer. This variometer also has the additional function of a coupling changer. By means of its use the wave length 0t an oscillator or radio transmitter may be continuously varied over a wide range and the change in coupling due to variation in wave length may be automatically compensated for. An important feature is that. these results maybe obtained by the manipulation of a single movable element.

it further object. is ,to provide means whereby the input and output couplings in an oscillator with an antenna or other circuit will assume at each wave lengtha value closely approximating the optimum value for that wave length.

A further object is to provide signaling apparatus containing all of the above and other advantageous features. The invention is not limited to the particular circuits illustrated, but may be in whole or part embodied in other arrangements.

For a detailed description oi the invention reference is made to the accompanying drawings wherein Fig. 1 represents a vacuum tube oscillating into an antenna and having a variable condenser connected between the grid and the anode; Fig. 2 is a typical curve representing the variation in power output with wave length of an oscillator of the type illustrated in l ig. l whereto improvements constituting this invention have not been applied; Fig. 3 represents an oscillation generator of a slightly diil'erent type; Fig. 4, a vacuum tube oscillating into an antenna and having a variable condenser shunted across the primary plate coil; and Fig. 5 is a perspective view of the antenna variometer and its associated coils such as is preferably used in Fig. 4.

Referring to Fig. 1, an antenna circuit '1 includes inductance coils 2 and 3 which are coupled respectively to coils l and 5 in the output and input circuits respectively of the vacuum tube 6, which comprises a suitable highly evacuated vessel having a hot filamentary cathode 7, an anode 8, and an impedance varying element 9 in the form of a grid. A stopping condenser 10 is included in the grid or input circuit and a high resistance leak path 11 is connected between the grid and the cathode. The antenna is here the frequency determining circuit of the oscillator. If the natural frequency of the antenna circuit 1 is varied in any suitable manner, as by varying the inductance of the coils 2 and 3 over a considerable range of values, as for example from about 240 meters to 575 meters, the power output 01- the oscillator will vary widely and irregularly as the wave length varies unless the condenser 12, or its equivalent, is provided.

Fig. 2 illustrates this variation. The Wave length is plotted along the horizontal axis, While the power in the antenna (PR) is plotted along the vertical axis. (I=antenna current, R=antenna. resistance.) Measurements of the power at wave lengths corresponding to each of the points a, Z), 0, (1, etc., were taken'and the curve of Fig. 2 thus obtained. lVith the particular arrangement whose characteristics are illustrated by this particular curve, oscillations did not not occur below a wavelength of about 240 meters and ceased above about 575 meters. It has been discovered that the points of minimum power output, correspond to multiples of some wave length which in the present instance,appears tobe approximately 190 meters, the multiple points being v the associated leads.

oscillate at a parasitic frequency determmed by this circuit, and in fact when the antenna 380 meters and 570 meters.- From an examination of a number of such curves taken under various conditions, it has been found that although the ratio between maximum and minimum power in a given instance varies widely, the curves all show the common characteristic of minimum power at approximate multiples of some wave length.

It has also been found that this wave length appears to be the'natural wave length ofsome frequency determining circuit inherent in the arrangement bemg tested. For example in Flg. 1, this lnherent wave length is determined bythe electrical constants of.

the coils 4 and 5, and the grid-plate capacity of the tube, together with the capacity of The systemtends to circuit is opened such parasitic oscillations will usually occur. The theory in accordance with which the power output at the desired frequency is caused to depend upon the V relation of the desired frequency" to some parasitic frequency of the circuit, is not precisely understood. The existence of such a relation, however, has been adequately proven by experimental investigation. I

eferring again to Fig. 1, the variable capacity 12 connected between the grid and the plate of the oscillating tube comprises one means for preventing the absorption'of energy by the parasitic oscillations. "When,

at a certain wave length as for example 360 meters, the power output falls to a low value, by connecting in the condenser 12 and ad justing it to some low value of capacity, the natural frequency of the interior circuit of the tube is changed to such a value that the power output increases. Ordinarily it will be sufficient for the condenser 12 to have a very small maximum capacity. By properly adjusting the capacity 12 at each readjustment of the wave length, the power output may be made substantially constant at every wave length at which oscillations will occur and approximately equal to the maxi-' mum power at any wave length.

e In the modified circuit arrangement of circuit which'determines the frequency of. parasltic oscillations, compr1ses the lnternal' grid-anode'capacity and the coils 2 and 5. The condenser 12 is utilized in this circuit in a manner similar to Fig. 1.

Fig. 4 comprises a circuit which in its principal features is the same as that of Fig. 1. The elements having applied thereto the reference numerals 4 to 11 inclusive, perform similar functions. Such systems are usually grounded at the cathode, as shown. The antenna circuit 1 is the principal frequency determining circuit and includes a variable inductance 16, of a novel form. Inductance 16 includes coils or groups of turns 17 and 18 which are fixed relatively to each other and the coils or groups of turns 19 and 20 which latter are fixed withrespect to each other but maybe rotated with respect to 17 and 18. The construction and relative ,arrangement of these coils is more fully illustrated in Fig. 5. Coils 17 and 18 are wound in parallel planes and 19 and 20 are likewise' wound in parallel planes'an d mounted spindle 22. l/Vhen the planes of these four coils are parallel as occurs'in one position,

the coil 17 is adjacent coil 19 and coil 18 is adjacent coil 20 thereby producing a maximum inductance, including the self-inductance of the coils and the mutual inductances between them, for the whole combination. When the coils 19 and 20 are rotated their respective mutual inductances with coils 17 and 18 vary'substantially in accordance with the cosine of the angle of displacement. The coils 4 and 5 are wound adjacent the coils 17 and l8 respectively, and in fixed relation thereto.. The mutual inductance between'coils 4 and 17 is fixed while that between coils 4 and 19 varies in accordance with their respective position. A similar condition exists in respect to coils 5, 18 and 20. The coils 4 and 5 will, in general, be only slightly coupled to each other by being each in the field of the other. The tendency of the interior oscillations to occur is, however, practically independent of direct coupling between coils 4' and 5 provided it is not too large which would be the case if coils l7 and 18 were very short and close together and coils 4 andv5 were closely adjacent thereto. The grid orinput coupling of the antenna circuit with the tube depends principally upon the relationship and relative number of turns of coils 4, 17 and 19 while the output or plate coupling depends principally upon the relationship of the coils 5, 18 and 20. The relative number. of turns in coils 17, 18, 19 and 20 may vary for different systems. It will be noted that when the natural frequency of the antenna circuit is increased by decreasing the inductance, the grid and the plate couplings between the antenna circuit 7 and the tube circuits will be decreased. 1 This action is important for if the couplings were to remain the same, increased natural frequency of the antenna circuit would cause increased voltages to be induced as a result of the two couplings before referred to, and henceinferior operation would result at some frequencies, thereby causing cessation of oscillations, or decrease in power output. Coils 4c, 5, 17 and 18 may be mounted on any suitable support and coilsa and 5 may or may not have separate attachments for producing variable coupling with respect to'coils 17 and 18 but all are preferably wound on one cylindrical tube of insulating material (not shown) Instead of connecting a condenser between the grid and the plate as in Fig. 1, a condenser21 is shunted across the plate primary coil 5. This condenser servestoso change the constants of the interior circuit as to prevent the absorption of-power by interior oscillations. This is due to the fact that a variation in the condenser 21 causes a corresponding variation in the eiiective in ductance of the plate circuit of the tube. At some positions of adjustment, the react-ance of the plate circuit of the tube for the interior oscillation frequency will become a capacity rea-ctance, while in other positions of adjustment the inductive reactance will be decreased. In some instances it may be the decreased inductive reactance of the output circuit at the parasitic frequency which reduces thetendency for parasitic oscillations to occur, and in other instances it may be. that the frequency at which the parasitic oscillations tend to occur is so changed that they are not troublesome. In certain circuits the improved results obtainable may be due to a combination of these effects. The idea of regulation of the constants of the parasitic oscillation circuit appears to be common to all explanations of the resulting phenomena.

The condenser 21 also has another important advantage. This is due to its eifect in improving the power factor of the plate current. Since the complete and exact theoretical demonstration of this improvement is complicated, it will be sufficient to explain it, in part, briefly, as follows: The action of the tube is similar to that of a high frequency generator connected between the anode and the cathode whose generated voltage is a function of the grid potential. This generator may be regarded as driving current through the circuit comprising the internal impedance of the tube and the external impedance of the output circuit.

Since the coil 5 acts as an inductive reactance, due to the leakage reactance, the current through the tube will be lagging behind the driving voltage. When, however. the condenser 21 is includedin shunt with the coil 5, a leading component of current will be superimposed upon the component through the coil 5. The algebraic sum of these components, when added, results in a current through the tube which is more nearly in phase with the driving voltage. Sincewave energy transferred from the output circuit to the input circuit must be returned to the input circuit in a certain phase relationship in order to secure the best oscillating condition, the condenser 21 offers the additional advantage of a phase regulater of the wave energy which is transferred from the output circuit to the input circuit of the vacuum tube.

The value of this invention, however, consists in the important useful results achieved by the means herein described or the equivalent thereof rather than in the correctness or incorrectness of the theory advanced in attempting to explain these results.

' In practice the wave length is changed by rotating the coils 19 and 20' by means of the spindle 22. lVhen the desired wave length is attained, the condenser 21 is then adjusted, if necessary, to such a value as will produce the maximum high frequency powor in the antenna. When a very exact wave length is desired a readjustment of spindle 22 and condenser 21 may be necessary. For any given installation a table may be provided from which may be read off directly, the proper adjustment of the condenser 21 for a particular wave length, or, the wave lengths may be marked on the scale of the antenna coil and the condenser 21. In general, however, a given table or Wave length marking will apply only to a given antenna or antennae of identical constants.

It is sometimes desirable to so design coil 5 and to so select condenser 21 that they form a closed loop resonant at approximately the double frequency of the desired antenna current. This acts to exclude any large component of this double frequency from the antenna A- suitable plate current source 23 may be connected with the circuit in any desired manner, as for example in shunt to a condenser 24 which is of large capacity. Suitable means may be provided whereby the oscillations produced by the oscillator may be started, stopped, varied or modulated in accordance with a code, speech, or other signals which are to be transmitted. Means for accomplishing these purposes, being well known in the art, need not be described here other than to say that any suitable means may be utilized.

The subject matter disclosed in Fig. 5 is pended claims.

What is claimed is: 1 Ano-scillation generating discharge device comprising a frequency-determining circuit, inductance means in said frequencydetermining circuit having four groups of turns, an input coupling coil for said device, and an output coupling coil for said device, said coils being in fixed relation to two of said groups of turns and in variable relation to two other of said groups of turns.

2. Anoscillator device having input and output circuits and including a'combined variomcter anda coupling transformer, said variometer comprising two pairs of relatively fixed groups of turns, said pairs being in variable relation to each other, an input circuit coil and. an output circuit coil, said coils being each arranged adjacent one group of one of said pairs.

3. A radio transmitting system comprising an antenna circuit which includes fired windings and movable windings, a space discharge device having an anode, a cathode and a grid, a grid-cathode circuit including a winding fixedly coupled to said fixed antenna windings and variably coupled to said movable antenna windings, an anode-cathode circuit including a winding fixedly coupled to saidfixed antenna windings and variably coupled to .said movable antenna windings, and a variable condenser connected acrossthe winding of said anode-cathode circuit.

4. A variometer and transformer comprising a work circuit winding having a portion relatively movable with respect to an energy transfer circuit portion, and another winding fixed with respect to one of said portions, the movement of said movable portion operating to change the total inductance of said work circuit winding and to change the coupling between said work circuit Winding and said energy transfer circuit winding to a value adapted to said changed inductance, in combination with a space discharge device for generating oscillations in a circuit including said windings.

5. A variometer and transformer in combination with a vacuum tube feed-back arrangement comprising a variometer proper and vacuum tube input and output coils sou-- pled thereto, a movablepart of said variometer proper being so related to a fixed part and to said coils that operation of said moving ot'said circuit, and a plurality of cir-v cuits electromagnetically coupled to said tuned circuit, said variometer comprising means for simultaneously and with one operation varying the tuning of said circuit and adjusting the coupling of each of said circuits to a value more appropriate to the varied tuning. c

7. A transmitting apparatus comprising an antenna circuit having seriallyincluded therein a first coil, a second coil, a third coil and afourth coil, and a thermionic repeater associated with said antennacircuit for the production of oscillations therein, said repeater having a grid circuit and a plate circuit, a coil in said grid circuit fixedlycoupled to sa'id first coil, and variably coupled to said second coil, a coil in said plate circuit fixedly coupled tos'aid fourth coil and variably coupled to said third coil, saidsec- 0nd and third coils being movable and fixedly related to each other.

8. In an osclllatlon generator, an input clrcuitcoll and an output circuit coil coupled to input ancl'output elements of a' space discharge device, a tuned circuit comprising fixed turns and movable turns, said movable turns being mounted on a rotatable member inside said fixed turns, a portion of said fixed turns being adjacent said input circuit coil and a portion being adjacent said output circuit coil.

9. An arrangement in accordance with claim 8 in which the nearest turns of the input and output circuit coils are spaced apart a substantial distance.

In witness whereof, I hereunto subscribe my name this 29th day of December A. D.,

f MILTON K. AKERs. 

